Hydraulic pump for machine tool drives



N0v.22,193s. -w. ERNST 2,137,448

HYDRAULIC PUMP FOR MACHINE TOOL DRIVES Filed Aug. 3. 1954 2 Sheets-Sheet 1 Nov. z2, 1938. w. ERNST 2,137,448:

HYDRAULIC PUMP FOR MACHINE TOOL DRIVES WALTER ERNST,

Patented Nov. 22, 1938 aimais HYDRAULIC PUMP Fonl MACHINE 'roo DRIVES l Walter Ernst, Mount Gilead, 0hio, assigner, by mesne assignments, to The Hydraulic Press Corporation, Inc., Wilmington, Del., a corporation of Delaware I Application August 3, 1934, Serial No. 738,320

9 Claims. (Cl. (S0-52) s PATENT OFFICE This invention relates to hydraulic pumps and circuits and, in particular, to such pumps and circuits as are adaptable to the driving of machine tool feeds and other similar drives. v

One objectpf my invention is to provide a hy- 4draulic pump with "a bored pintle so lconstructed as to. provide a back pressure to the double-acting motive piston which operates the machine tool feed or other suitable devices.

Another object is to provide a hydraulic pump having a' pintle with intake and discharge bores, the pintle being so constructed that the pump tends to discharge a greater amount of fluid to one s ide of a double acting motive piston, than can be returnedto the inletof the pump from the opposite side of the piston, so as to provide a back pressure on thepiston in `order-to prevent creeplngf or uneven motion due to variations in the load. l

Another object Vis to provide such a circuit wherein the pintle hastwindischarge passages and twin intake'pa'ssages, the partition between the intake passages being asymmetrically placed, one intake passage communicating with a fluid tank for supplying make up fluid, whereas'the other intake passage and the discharge passages communicate with opposite sides of the motive or operating piston, the latter being used to operate any suitable devices; the pump thus discharging more fluid toward the one sideof the piston than can be returned from `the opposite side of the plstonpto the lintake passage connected thereto, the excess fluidbeing discharged through any suitable means, as through a relief valve.

In thedrawings:

Figure 1 is a diagrammatic representation of the hydraulic circuit of my invention,.showing in cross section thepintle construction and connections thereof to the double-acting operating or servo-pistonby way of a control valve.

Figure 2` is a central vertical cross section through the vpump shown in part in Figure l, and showing the'pintle construction thereof.

The problem faced by the applicant was to devise a hydraulic'circuit whereby a servo-piston could be moved smoothly or flrmly locked in a given position, this servo-piston being particularly used for feeding tools. In previous arrangements of this sort, employing a single-acting piston, the piston has had a tendency to creep under varying resistance'as well as to jump when the cutter or drill breaks through thework piece. This is. liableto break the tool orproduceA chatter marks on the work piece. ,Double-acting:

pistons have been devised in the prior art to overyhores 5 and E impa' come this dililculty, but resulted in very complex and costly apparatus or else in unsatisfactory operation. against one side of the servo-piston by throttling the fluid discharged therefrom has, for example, resulted in excessive heating and waste of power due to the motion of the high velocity fluid through the throttling valve.

The provision of a constant delivery pump to A feed fluid to one sideof the operating or servopiston and a variable delivery pump with a bypass arrangement to feed the other side thereof results in a complex and costly mechanism, as Well as in the waste of a large amount of the fluid pressure developed, because of the fact that at slow feeding speeds, much of the pump discharge must be by-passed. i

In the applicant's solution of the problem, as shown in detail in the drawing of Figure 1, a single variable delivery pump suflices to provide fluid pressure for both sidesof the double-acting piston. The applicant's arrangement consists, in general, of a variable delivery pump, represented diagrammatically in Figure 1, and having a rotary cylinder barrel I, and a pintle 2 of special construction. The detailed construction of the pump is immaterial, since any suitable type of cylinder and pistonconstruction may be used in com- The attempt to create back pressure bination with the pintle 2, such as that shown in In the central plane of the pump, that is the.

plane passing through the axis of` the cylinder bores, the intake bores 3 and 4 open respectively into pintle cut-outs 'I and 8. The discharge bores 5 and 6, on the other hand, open into a pintle cut-out 9. Asthe cylinder barrel I of the pump rotates in the usual manner, its cylinder ports 31 are presented successively to the pintle cut-outs 1, 9 and 8, assuming a clockwise rotation of the-cylinder barrel.

It will be observedv .that both of the discharge A heir contents 'into the common discharge c yt outra, the partition Hl being spaced'away fromfthe cylinder barrel. In contrast to this. thev intake bores I and 4 open intov separate intake cut-outs 1 and 8, these being separated by the partition II, the latter being placed in an eccentric position so as to make the angular extent of the intake cut-outs 1 and 8 decidedly unequal as measured from the axis of rotation I2 of the cylinder barrel. The exhaust and intake cut-outs are separated from one another by the transverse partition member I 3 which completely separates the opposite sides of the pump.

The angular extent of the intake port 8 as shown in Fig. 1 amounts-to approximately 95. The governing feature of the return to the inlet 8 resides in the fact that the amount of fluid returned to the inlet will depend upon what portion of arevolution an inlet 31 will remain in communication with the inlet 8. If in Fig. 1 measuring from 'a point at which an inlet 31 begins to communicate with inlet 8 until the same just passes the portion I I it will be found that the extent of communication of an inlet 31 with inlet 8` amounts to about 119. These figures are only approximate, since the partitions II and I3 th'emselves have a certain amount of angular extent,

measured from the axis of rotation I2 of the pricharge conduit I9 of the'pump. The latter runs from the discharge bores 5 and S at the end of the pintle 2 to the middle chamber 2I .of the control valve 2li. 'Ihe end chambers 22 and 23 Aof the latter are interconnected' by the conduit 24, which in turn is connected to the intake conduit 25 leading to the intake bore 4 at the end of the pintle 2.

The control valve 20 serves to reverse the direction of the iluid discharged by the pump, and contains a reciprocable valve rod 25 having spaced heads 21 and 28 whichare shifted to and fro by the hand knob 29. The intermediate chamber 30 oi' the control valve 2li is connectedby the conduit 3I to one end of the operating piston cylinder 32. Ihe latter is provided with the double-acting piston 33 having the piston rod 34 movable in either direction according to the direction of the uid admitted to its cylinder 32. The opposite end of the cylinder 32 is provided with the conduit 35 leading to the intermediate chamber 36 of the control valve 2l.

The pump shown in part in Figure 1 is shown in greateidetail in Figure 2. In addition to the pintle 2, previously described in detail, the cylin' der barrel I contains the cylinder ports 31 leading to the radial cylinder bores 38, within which the pistons 3! are arranged to reciprocate. 'I'he latter are provided with crossheads 40, engagingl supported by the shift ring 45.

, be moved to and fro either by hand or by suitable servomotor mechanism, known to those skilled in the art, thereby varying 4,the separation of the the axis of rotation. of the secondary rotor 44;

This rotation of the two rotors I and 44 upon independent and separated axes causes the pistons 39 to reciprocate by reason of the engagement of their crossheads 40 with the guide blocks 42, in a manner well known to those skilledl in the art.

In the position of the valve heads 21 and 28 shown ,in Figure 1, the uid will be discharged into the righthand end of the operating cylinder 32, in the direction of thearrow, and withdrawn from. the lefthand end thereofthrough the conduit 35. 'I'his causes the piston rod 34- to move to the left, in the direction shown'by the arrow. By shifting the control valve 20, the direction of ow may be reversed, thus causing the operating piston 33 and the piston rod 34 to move to the right.

In the circuit shown in Figure 1, the feature of separating the intake ports 3 and 4 by the partition II and the connection thereof to 'the tank I5 and control valve 20 respectively through the conduits I4 and 25, results in a tendency for a greater amount of fluid to be discharged into one side of the operating cylinder 32 through the pipe I3 than is withdrawn from the other side through the pipe 25. The intake pipe I4 serves as a "makeup pipe for the admission of fluid to supply any deficiency which' may occur in the various cylinders.

This inequality of pressure on opposite sides of' the operating piston head 33 causes the latter to move until the pressures are balanced on opposite sides thereof, or until the resistance'encountered balances this pressure. Excess pressure is taken care of by the discharge of fluid through the pipe I8 and relief valve I 1 into the tank 15 by way of the discharge pipe I6. l

In the operation of the pump and circuit of my invention, the fluid will travel in the direction shown by the arrows when the'parts are arranged the latter. With this arrangement, the operating piston 33 is crowded in such a manner that a positive back pressure is created on its exhaust side, since the pump does notv take as much iiuid out of the operating cylinder 32, as it attempts 'to put into this cylinder, owing to the additional make-up iiuid received from the tank I5 through the conduit I4. v

It will be understood that I desire to comprehend within my invention such modiflcations as may be necessary to adapt it to varying conditions and uses. Y

Having thus fully described my invention what I claim as new and desire to secure by Letters Patent is: A

1. In combination, a hydraulic pump having pumping means therein and a pintle with an out-` let port and two inlet ports, a hydraulic motor having its opposite iiuid connectionsto said outlet port and to one of said inlet ports respectively, a source of working tluid connected to the other of said inlet ports, the discharge capacity of the pumping means connected to said outlet port being greater than'the intake capacity of the pumping means connected to said first-mentioned inlet port, whereby" said pump will tend to supply a A greater amount of fluid to one side `of said motor than ,is withdrawn fromthe other side thereof,

7o letportnnda and relief means connected to discharge the' excess fluid from said outlet port.

2. In combination, a hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports, a double-acting motive piston having its opposite sides connected to said outlet port and to one of said inletports respectively, relief. means connected to said outlet port, a source o! iluid connected to the other of said inlet ports, the discharge capacity of the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said first-mentioned inlet port, 'whereby said' pump will tend to supply a greater amount of iluid toene side of said piston than is withdrawn from the other side thereof.

3. In combination, a hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports of unequal circumferential extent, a double-acting motive piston having its opposite sides connected to said outlet port and to one of said inlet ports respectively, means for supplying fluid to the other inlet port, the discharge capacity of the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said first-mentioned inlet port, whereby a back pressure will be built up against said double-acting piston, and relief means connected to discharge the excess fluid from said outlet port.

4. In combination, a variable delivery hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports, a

double-acting motive piston having its opposite sides connected to said outlet port and to one of said inlet ports respectively, means for supplying iluid to the other inlet port, the discharge capacity of the pumping means connected to said outlet port being greater than the'intake capacity of the pumping means connected to said first-mentioned inlet port, whereby said pump will tend to supply a greater amount of iluid to one side of said piston than is withdrawn from the other side thereof, and means responsive to the attainment of a predetermined pressure for discharging the excess nuid when said predetermined pressureiis exceeded.

5. In combination, a hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports of unequal circumferential extent, a double-acting motive piston having its opposite sides connected to said outlet port and to one .of said inlet ports respectively, a source of working fluid connected to the other oi.' said inlet ports, the discharge capacity or the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said firstmentioned inlet port, whereby said pump will tend to supply a greater amount of fluid to one side o! said piston than is withdrawn from the other side thereof, and pressure-responsive relief means adapted to discharge the excess fluid from the circuit of said piston when the pressure in said circuit exceeds @predetermined amount.

6. In combination, a hydraulic pump havingy pumping means therein and a pintle with an outpair oi inlet ports separated from -of the pumping means connected to said firstmentioned inlet port, whereby said pump will tend to supply a greater amount of fluid to one side of said piston than is withdrawn from the other side thereof, and means for reversing the directionV of ow of said uid between said pump and said piston.

7. In combination, a variable delivery hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports, separate longitudinal bores communicating with said outlet port and each of said inlet ports respectively, a double-acting motive piston having its opposite sides connected to said outlet port and to one of said inletports respectively through said bores, means for supplying fluid to the other inlet port, the discharge capacity of the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said rst-mentioned inlet port, whereby a back pressure will be built up against said double-acting piston, and relief means connected to discharge the excess fluid from said outlet port.

8. In combination, a variable delivery hydraulic pump having pumping means therein and a pintle with an outlet port and a pair of inlet ports, separate longitudinal bores communicating with said outlet port and each of said inlet ports respectively, a double-acting motive piston having its opposite sides connected to said outlet port and to one of said inlet ports respectively through said bores, means supplying uid tothe other inlet port, the discharge capacity of the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said first-mentioned inlet port, whereby a back pressure will be built up against said double-acting piston, and pressure-responsive relief means adapted to discharge the excess uid delivered to said piston when the pressure thereof exceeds a predetermined amount. p

9. In a pumping combination, a hydrauli pump circuit including pumping means connected to two inlet ports and-an outlet port, a control valve interposed between the outlet port and one inlet port of said pump, a iluid supply tank connected to the other inlet port, an operating piston connected to said control valve, and a return line with a relief valve therein extending between the outlet port and the supply tank, the discharge lcapacity of the pumping means connected to said outlet port being greater than the intake capacity of the pumping means connected to said nrstmentioned inlet port, whereby the operating piston is crowded and a positive back pressure is created on its exhaust side by reason'of the fact that the pump takes less iluid away from the piston than it attempts to supply thereto.

WALTER ERNST.' 

